The present invention relates to a semiconductor device and a method of fabricating the same.
Recently, the electrical thickness of a gate insulating film decreases as the micropatterning of MOSFETs advances, and this poses the problem that a gate leakage current increases. To suppress this gate leakage current, therefore, a method which uses, as a gate insulating film, a high-dielectric-constant film having a relative dielectric constant higher than that of a silicon dioxide (SiO2) film is proposed. A hafnium silicon oxynitride (HfSiON) film is an example of this high-dielectric-constant film.
The hafnium silicon oxynitride (HfSiON) film is formed by, e.g., forming a hafnium silicate (HfSiOx) film on a semiconductor substrate, and nitriding the hafnium silicate (HfSiOx) film by doping nitrogen (N) into it.
In the hafnium silicate (HfSiOx) film, however, the bonding force between atoms is weak. Therefore, when nitrogen (N) is doped, bonding hands for bonding atoms are disconnected, and a large number of defects (holes) are formed.
When this hafnium silicon oxynitride (HfSiON) film is exposed to an oxidizing ambient or the atmosphere, atmospheric oxygen (O2) or the like is activated by hafnium (Hf) as a catalyst, and oxygen radicals are produced. These oxygen radicals easily invade the hafnium silicon oxynitride (HfSiON) film or a semiconductor substrate.
Consequently, an interface insulating film having a low dielectric constant is formed between the hafnium silicon oxynitride (HfSiON) film and semiconductor substrate. This decreases the effective relative dielectric constant of the gate insulating film or increases the electrical thickness of the film.
In addition, since oxygen (O) replaces nitrogen (N) in the hafnium silicon oxynitride (HfSiON) film, nitrogen (N) is released from the hafnium silicon oxynitride (HfSiON) film.
As a consequence, the hafnium silicon oxynitride (HfSiON) film is separated into silicon dioxide (SiO2) and hafnium dioxide (HfO2), and these compounds crystallize. This decreases the heat resistance. Also, boron as a dopant readily breaks through the hafnium silicon oxynitride (HfSiON) film and diffuses into the semiconductor substrate. Furthermore, dielectric breakdown easily occurs, and this shortens the life of the gate insulating film.
These problems produce fluctuation in gate threshold voltage and variations in transistor characteristics.
A reference concerning a method of forming an insulating film having a high dielectric constant is as follows.
Japanese Patent Laid-Open No. 2004-71696